1. Field of the Invention
The present invention relates to data communications. It is particularly suitable for power line communications (PLC) between locations having a common electrical distribution system.
2. Description of the Related Art
PLC, also known as Broadband over Power Line (BoPL), is a technology that encompasses transmission of data at high frequencies through existing electric power lines, i.e., conductors used for carrying a power current. Power current is typically transmitted through power lines at a frequency in the range of 50–60 hertz (Hz). In low voltage lines, power current is transmitted with a voltage between about 90 to 600 volts, and in medium voltage lines, power current is transmitted with a voltage between about 2,400 volts to 35,000 volts. The frequency of the data signals is greater than or equal to about 1 megahertz (MHz), and the voltage of the data signal ranges from a fraction of a volt to a few tens of volts. Data communication can employ various modulation schemes such as amplitude modulation, frequency modulation, pulse modulation or spread spectrum modulation.
An inductive coupler couples PLC signals to and from a power line. The inductive coupler has a high pass frequency characteristic. Therefore, a signal attenuation or path loss through the inductive coupler may be excessive below a lower cutoff frequency of the inductive coupler.
It is desirable to provide for PLC communications over a range of frequencies that extends below a lower cutoff frequency of an inductive coupler.